This is very annoying. I tried to cancel an award reservation that was booked online and got this message EVERY TIME:

Due to the special conditions associated with this reservation you may view, but not change it within this website. Please return to where the reservation was originally confirmed to make modifications or cancellations.

If you are trying to modify or cancel a Gold Passport Award reservation please call 1-800-30-HYATT.

Why? It's only a simple cancellation that is within the cancellation period.